No abstract

This article presents a method for preparing and testing the piezoelectric properties and stability of cellular electret based on polypropylene (PP). Introducing 5% mineral filler as a mixture of crystalline silica, colloidal silica, and kaolin to isotactic polypropylene followed by a film stretching process resulted in the formation of a composite cellular structure. To manufacture electrets, the films were polarized at a constant electric field in the range from 100 V/lm to 125 V/lm, in a climatic chamber heated up to 80°C. The durability of the electrets was determined using thermostimulated discharge currents and approximate calculations of depolarization process activation energy. For electrets made of cellular films, the depolarization temperature T m at which the density of the discharge current assumes the highest value was $108°C and the activation energy was 6.25 eV. The response of the polarized composite film to mechanical stress expressed as the piezoelectric constant d 33 was about 3 times higher than for a-PP film of the prevailing atactic phase and poly(vinylidene fluoride) film without a cellular structure. In the range of stress of 1 kPa to 120 kPa it was 135 pC/N for lower stresses and 60 pC/N for higher stresses.

The low-density polyethylene (PE)/waste paper composites with different components ratio were prepared by extrusion. The photochemical stability of these samples and crystallinity degree of PE in blends were studied using ATR-FTIR spectroscopy. The thermal properties of composites were estimated by thermogravimetric analysis. Moreover, the morphological changes were observed by SEM. It was found that after long-term exposure to UV (100 h) composites undergo more efficient photo-oxidative degradation when compared with pure PE. Also the thermal stability of composites obtained is lower than that in PE. The results indicate that such a material is characterized by high susceptibility to environmental decomposition.

No abstract

Extrudate properties are largely shaped by the thermal and rheological phenomena occurring in the plasticizing systems of extruders, the channels and die of the extrusion head, the calibrator, and to a lesser extent, in other parts of extrusion lines. These phenomena are affected by barrel and screw design, the type of material being processed, its granulometry, and the technological parameters of the extrusion process. Studies were carried out on the dependency of the output and selected mechanical properties of a plasticized poly(vinyl chloride) (PVC) extrudate on rotational speed of the screw, the width of the feed opening, and the length of the pellets of input polymer. It was found that the parameters tested were affected to the largest extent by the screw-rotational speed. A fivefold increase in screw-rotational speed resulted in a few hundred percent increase in the output and a several dozen percent increase in the yield strength of the extrudate, with the highest value obtained for pellets whose length was close to their diameter. Reduction of the width of the feed opening from 1.0 to 0.6 D resulted in a slight increase in the yield strength and tensile strength. High output, yield strength, and tensile strength values of PVC are most readily achieved at high screw-rotational speed, the smallest width of the feed opening, and the length of pellets close to their diameter. C